Conventionally, various devices have been conceived as a radiation imaging device for imaging an internal structure of an object by making radiation transmit through the object. A commonly-used radiation imaging device is configured to take a radiation projection image by irradiating radiation to an object to make the radiation transmit through the object. In such a projection image, shading appears depending on the ease of permeation of radiation, which represents the internal structure of the object.
With such a radiation imaging device, only an object having a property capable of absorbing radiation to some extent can be imaged. For example, soft biological tissues hardly absorb radiation. Even if it is attempted to image such a tissue with a general device, almost nothing will be reflected on the projection image. When attempting to image an internal structure of an object that does not absorb radiation as described above, there is a theoretical limit in a general radiation imaging device.
Under the circumstances, a radiation phase-contrast imaging device configured to image an internal structure of an object utilizing a phase-contrast of transmitted radiation has been proposed. Such a device is configured to image an internal structure of an object using Talbot interference.
Talbot interference will be described. From the radiation source 53 shown in FIG. 11, phase-aligned radiation is irradiated. When making the radiation transmit through a phase grating 55 which is in a streak form, the image of the phase grating 55 appears on the projection surface which is apart from the phase grating 55 by a predetermined distance (Talbot distance). This image is called self-image. The self-image occurs only at the position where the projection surface is separated from the phase grating 55 by the Talbot distance, and the self-image is not just a projection image of the phase grating 55. The self-image is configured by interference fringes caused by interference of light. The reason that the self-image of the phase grating 55 appears at the Talbot distance is that the phase of radiation generated from the radiation source 53 is aligned. When the phase of radiation is disturbed, the self-image appearing at the Talbot distance is also disturbed.
The radiation phase-contrast imaging device is configured to image an internal structure of an object utilizing self-image disturbance. It is assumed that an object is placed between the radiation source and the phase grating 55. Since this object hardly absorbs radiation, most of the radiation incident on the object exits to the phase grating 55 side.
The radiation has not completely transmitted through the object as it is. The phase of the radiation changes when the radiation transmits through the object. The radiation exited the object transmits through the phase grating 55 with the phase changed. Observing the radiation on the projection plane arranged at the Talbot distance, a disturbance of the self-image of the phase grating 55 is recognized. The degree of disturbance of the phase grating 55 represents the radiation phase change.
The specific magnitude of the phase change of the radiation that transmitted through the object varies depending on where the radiation transmits through the object. If the object has a homogeneous structure, the change of the radiation phase remains the same no matter where the radiation transmits through the object. In general, however, an object has some internal structure. When making radiation transmit through such an object, the phase change does not remain the same. Therefore, when the phase change is known, the internal structure of the object can be known. The phase change can be known by observing the self-image of the phase grating 55 at the Talbot distance. The observation of the self-image may be carried out with a radiation detector placed at the Talbot distance (see, e.g., [9] International Patent Laid-Open Publication No. 2009104560, hereby incorporated by reference).